Refined Unit Cell Research Articles

Phase transitions as a function of temperature in BIMGVOX

Phase transitions in BIMGVOX, Bi 2 Mg x V 1-x O 5.5-3x/2-δ , have been studied using a combination of a.c. impedance spectroscopy, differential thermal analysis and variable temperature X-ray powder diffraction. Two composition regions were examined. In the first, below x = 0.10, phase transitions associated with the α, β and γ-phases are observed. In the second region above x = 0.10 the γ'↔ γ transition is clearly observable. Trends in the refined unit cell parameters were particularly indicative of the phase transitions. The results are compared to those obtained for parent compound Bi 4 V 2 O 11-δ .

The crystal structure of molybdomenite, PbSeO3

The crystal structure of molybdomenite (PbSeO 3 ) from El DragOn mine (Bolivia) was refined in the space group P2 1 /m, using single-crystal X-ray diffraction data, to R F =0.049. The refined unit cell parameters are a = 4.5437(7), b = 5.5137(8), c = 6.634(1)A, β = 106.547(7)°. Molybdomenite is the lead selenite and is isostructural with scotlandite, the lead sulphite, PbSO 3 , with Se 4 + playing the same role of S 4 + in the latter. The structure of molybdomenite can be described as stacking of complex structural slabs along (100). In molybdomenite lead is nine-fold coordinated (average Pb-O 2.78 A) and selenium form a trigonal pyramid with three oxygens (average Se-O 1.71 A).

Powder diffraction of the cubic perovskite Ba0.5Sr0.5Co0.8Fe0.2O3−δ

X-ray powder diffraction data for Ba0.5Sr0.5Co0.8Fe0.2O3−δ are reported. The powder was prepared using a metal-EDTA complexing method. The XRD data could be fitted with a primitive cubic unit cell in space group Pm3m (No. 221). The Rietveld refined unit cell parameter is ac=0.398 30(3) nm with Z=1 and Dx=5.75 g/cm3.

X-ray powder diffraction analysis of 2-exo-(β-pyridyl)-6-exo-phenyl-7-oxa-1-azabicyclo[2.2.1]heptane

The X-ray powder diffraction pattern for a bridgehead heterocyclic system was determined. 2-exo-(β-pyridyl)-6-exo-phenyl-7-oxa-1-azabicyclo[2.2.1]heptane, C16H16N2O, is triclinic with refined unit cell parameters a=1.1012(2), b=1.3950(2), c=1.0074(3) nm, α=111.09(2)°, β=104.97(2)°, γ=77.38(2)°, V=1.3813(3) nm3, Z=4, and Dx=1.212 g/cm3 with space group P-1 (No. 2).

X-ray powder diffraction data for In3.85Zr2.80Sn0.35O12

X-ray powder diffraction data for In3.85Zr2.80Sn0.35O12 are reported. The powders were prepared using a wet-chemical precipitation method. The XRD data could be fitted with a rhombohedral unit cell in space group R3 (No. 148). The Rietveld refined unit cell parameters are a=0.951 49(2) nm and c=0.889 51(2)nm in a hexagonal setting with Z=3 and Dx=6.69(1)g/cm3.

On the solubility of chromium sesquioxide in uranium dioxide fuel

Chromium sesquioxide doped uranium dioxide systems with a variety of initially added Cr 2O 3 amounts were prepared under different sintering conditions. The solubility limit of Cr for each sintering condition is derived from the measured content of the dopant dissolved in the UO 2 matrix using electron probe microanalysis (EPMA). It is found that the solubility of chromium in a uranium dioxide system for these series sintered at 1600, 1660 and 1760 °C is limited to respectively 0.065±0.002, 0.086±0.003 and 0.102±0.004 wt% Cr. The lattice parameters of the different Cr 2O 3 doped fuels have been examined with X-ray diffraction (XRD). The XRD peaks of the samples sintered at 1760 °C as well as a UO 2 reference without Cr, prepared under the same conditions, were measured and a value for the lattice parameter a for each sample was obtained using the unit cell refinement method. A slight contraction of the lattice parameter is observed with increasing dopant content.

X-ray powder diffraction analysis of a nonlinear optical material N-(p-methoxy benzoyl)-N′-(p-methyl phenyl) thiourea

A nonlinear optical material, N-(p-methoxy benzoyl)-N′-(p-methyl phenyl) thiourea (C16H16N2O2S), has been characterized by X-ray powder diffraction. Experimental values of 2θ corrected for systematic errors, relative peak intensities, values of d, and the Miller indices of 94 observed reflections with 2θ up to 66° are reported. The powder diffraction data and the figure-of-merit are reported. The least-squares refined unit cell parameters are a=25.3291(3) Å, b=11.9478(1) Å, c=10.1407(4) Å, β=103.10(2)°, V=2988.97(6) Å3, Z=8, Dx=1.335(0) g/cm3, with space group P21(4).

X-ray powder diffraction analysis of a nonlinear optical material N-(p-methoxy benzoyl)-N′-(o-methyl phenyl) thiourea

A nonlinear optical material, N-(p-methoxy benzoyl)-N′(o-methyl phenyl) thiourea (C16H16N2O2S), has been characterized by X-ray powder diffraction. Experimental values of 2θ corrected for systematic errors, relative peak intensities, values of d, and the Miller indices of 90 observed reflections with 2θ up to 88° are reported. The powder diffraction data have been evaluated, and the figures-of-merit are reported. The least-squares refined unit cell parameters are a=26.7079(3) Å, b=6.7995(9) Å, c=19.2845(1) Å, β=121.39(4), V=2989.42(3) Å3, Z=8, Dx=1.334(8) g/cm3, space group P2(3).

Solid solutions Ln 10S 14+ xO 1− x (Ln:Ce, Nd) as possible pigments

The microstructure (via SEM, TEM), and color parameters of the solid solution (Ce 1− y Nd y ) 10S 14+ x O 1− x (0≤ y≤0.70) (0≤ x≤1) were investigated. The samples structure corresponds to the Pr 10S 14O type. The scanning electron micrographs (SEM) show small particle size (around 100 nm). The samples have been characterized by transmission electron microscopy (TEM) and associated techniques. The observed variation in the powder X-ray diffraction refined unit cell parameters is due to the variable oxygen content.

Powder diffraction data for borides Pd3B and Pd5B2 and the formation of an amorphous boride Pd2B

Powder diffraction data and refined unit cell parameters of two palladium borides were determined. For Pd3B (space group Pnma; Fe3C type) it was found that a=0.54602(3) nm, b=0.75596(4) nm, c=0.48417(4) nm and for Pd5B2 (space group C2/c; Mn5C2 type) a=1.27759(12) nm, b=0.49497(5) nm, c=0.54704(4) nm, β=97.049(7)°. Further, it was shown that the position of the principal scattering peak of the amorphous Pd2B fulfils the Nagel–Tauc criterion about glass forming ability.

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The phase relation studies in the Y2O3–Nd2O3 system has been established after slow cooling of the samples from 1400 °C. Three phase regions, namely a C-type cubic solid solution, a monoclinic solid solution and a biphasic mixture of these two phase fields were observed in this system. An important observation of this investigation is the stabilization of B-type monoclinic phase of Nd2O3 on substitution of about 10 mol% Y3+. A nominal Nd0.90Y0.10O1.5 composition from the monoclinic type solid solution phase region was characterized by the Rietveld refinement of the observed powder XRD data. The typical refined unit cell parameters for this nominal composition are: 14.2761(3), 3.6449(1), 8.9022(2) Å and β = 100.391(2)°, V = 455.62(2) Å3. The refined results confirm the monoclinic rare-earth oxide structure with Nd3+ with seven coordinated (capped distorted trigonal prism type) polyhedra and six coordinated (trigonal prism) polyhedra. The crystal structure is built from the edge sharing of these polyhedra. The striking observation of the refinement is that the Y3+ prefers six coordinated polyhedral site instead of randomly distributed over all the Nd3+ sites, which is accounted by the smaller ionic radii of Y3+ compared to the Nd3+ ions. The further details of the trend in phase relation in Nd2O3–Y2O3 system has been explained on the basis of the crystal structure and ionic radii of the metal ions.

Powder diffraction data for the germanides CoGe and Co5Ge7

Precise X-ray powder diffraction data are given for two germanides, CoGe and Co5Ge7. The refined unit cell parameters for CoGe are a=11.630(1) Å, b=3.8014(3) Å, c=4.9347(3) Å and β=100.889(8)° (space group C2/m, Pearson symbol mC16) with volume of the unit cell 214.24(2) Å3; the figures of merit are M20=96, F30=77 (0.0085, 46). The refined unit cell parameters for Co5Ge7 are a=7.6262(4) Å and c=5.8017(5) Å (I4mm, tI24) with volume of the unit cell 337.42(3) Å3; the figures of merit are M20=204 and F22=130(0.0068, 25). The dependence on composition of the unit cell parameters of CoGe is discussed in terms of specific defect structures.

Synthesis of Strontium Borophosphate, SrBPO5 by Solid State and Hydrothermal Methods and Characterisation

SrBPO5 was synthesized by a solid-state reaction reported and by a new solid state reaction using BPO4 as a phosphating agent. It was also obtained by a hydrothermal method. The structure of the compound was solved by Rietveld analysis before. The examination of X-ray powder diffraction data showed that, SrBPO5 is isostructural with CaBPO5 and BaBPO5. It crystallizes in the trigonal system in P3121 and the refined unit cell parameters are a = 6.8488(1), c = 6.8159(2) Å, Z=3 and Dm 3.77 g/cm3.

Powder diffraction data and Rietveld refinement for Y-doped (ZnO)5In2O3

Indexed X-ray powder diffraction data are reported for the homologous compound (ZnO)5(In1−xYx)2O3. The structures of (ZnO)5In2O3and of (ZnO)5(In1−xYx)2O3were refined by the Rietveld technique on the basis of the space groupR3¯m. Refined unit cell dimensions area=3.3285(1) Å,c=58.127(2) Å,V=557.71(3) Å3,Dx=6.11g/cm3,Rwp=10.52,RB=8.56 for (ZnO)5In2O3, anda=3.3505(1) Å,c=57.863(1) Å,V=562.53(2) Å3,Dx=5.97g/cm3,Rwp=9.05,RB=6.94 for (ZnO)5(In0.8Y0.2)2O3. The structure of (ZnO)5In2O3was shown to be isostructural with (ZnO)5LuFeO3.Y3+ions were determined to be arranged at the 3a-metal sites substituting forIn3+ions.

X-ray powder diffraction data for the ternary phases W5As2.5P1.5 and Ni4Nb5P4

The two ternary phases W5As2.5P1.5 and Ni4Nb5P4 have been investigated by X-ray powder diffraction. Precise data for the two compounds were collected using CuKα1 radiation over the range 11°–140° 2θ. Unit cell refinements (space group I4/m) led to a=9.4729(3) Å, c=3.2414(2) Å (Dx=13.16 gcm−3) with M20=127, F30=91(0.0092,36) for W5As2.5P1.5 and a=9.9304(4) Å, c=3.5243(3) Å (Dx=7.87 gcm−3) with M20=179, F30=138(0.0068,32) for Ni4Nb5P4.

Crystal structure and powder data of davidite-type La2Ti10.27Ga9.63O38

The structure type of La2Ti10.27Ga9.63O38 was revealed by a search-match using the PDF. A successful Rietveld refinement (Rp=8.9, Rwp=13.3, RB=4.20) confirmed the structure to be rhombohedral (space group R3¯, No. 148) with the refined unit cell parameters a=9.1878(1) Å, α=68.458(1)°, and V=646.374(1) Å3. The structure is compared to other compounds of the davidite type, and the observed and calculated powder data are given.

Barium hollandite-type compounds BaxFe2xTi8−2xO16 with x=1.143 and 1.333

Experimental X-ray powder diffraction patterns and refined unit cell parameters for two barium hollandite-type compounds, BaxFe2xTi8−2xO16, with x=1.143 and 1.333, are reported here. Compared to the tetragonal parent structure, both compounds exhibit monoclinic distortions that increase with Ba content [Ba1.333Fe2.666Ti5.334O16: a=10.2328(8), b=2.9777(4), c=9.899(1) Å, β=91.04(1)°, V=301.58(5) Å3, Z=1, ρcalc=4.64 g/cc; Ba1.143Fe2.286Ti5.714O16: a=10.1066(6), b=2.9690(3), c=10.064(2) Å, β=90.077(6)°, V=301.98(4) Å3, Z=1, ρcalc=4.48 g/cc]. The X-ray powder patterns for both phases contain a number of broad, weak superlattice peaks attributed to ordering of the Ba2+ ions within the tunnels of the hollandite framework structure. According to the criteria developed by Cheary and Squadrito [Acta Crystallogr. B 45, 205 (1989)], the observed positions of the (0k1)/(1k0) superlattice peaks are consistent with the nominal x-values of both compounds, and the k values calculated from the corresponding d-spacings suggest that the Ba ordering within the tunnels is commensurate for x=1.333 and incommensurate for x=1.143. High-temperature X-ray diffraction data indicate that the x=1.333 compound undergoes a monoclinic→tetragonal phase transition between 310 and 360 °C.

High-temperature powder x-ray diffraction of yttria to melting point

Powder x-ray diffraction data of yttria (Y2O3) were obtained from room temperature to melting point with the thin wire resistance heating technique. A solid-state phase transition was observed at 2512 ± 25 K and melting of the high-uemperature phase at 2705 ± 25 K. Thermal expansion data for α–Y2O3 (C-type) are given for the range 298–2540 K. The unit cell parameter increases nonlinearly, especially just before the solid-state transition. The x-ray diffraction spectrum of the high-temperature phase is consistent with the fluorite-type structure (space group Fm3) with a refined unit cell parameter a = 5.3903(6) Å at 2530 K. The sample recrystallized rapidly above 2540 K, and above 2730 K, all the diffraction lines and spots disappeared from the x-ray diffraction spectrum that suggests complete melting.

Solid-State Synthesis, X-ray Powder Investigation and IR Study of α-Mg 3[BPO 7

α-Mg 3[BPO 7] (low temperature form) which is isostructural with Zn 3[BPO 7] has been synthesized by the solid-state reactions of MgHPO 4.H 2O with MgCO 3 and H 3BO 3 at 1200°C, Mg 3B 2O 6 with MgCO 3 and (NH 4) 2HPO 4 at 1100°C, and MgO with B 2O 3 and P 2O 5 at 1100 with the molar ratios of 1:2:1, 1:3:2 and 6:1:1, respectively. The structure of α-Mg 3[BPO 7] was found to be orthorhombic (as already reported), with refined unit cell parameters of a=8·495(3), b=4·886(1) and c=12·565(4) Å; the space group is Immm with Z=4. The indexed X-ray powder diffraction data and the IR spectrum of α-Mg 3[BPO 7] are also given. The latter reveals trigonal planar coordination of boron.

Crystallite Sizes and Lattice Distortions of Gel-Spun Ultra-High Molecular Weight Polyethylene Fibers

A detailed method is reported for deriving the lattice distortions and crystallite sizes of ultra-high molecular weight polyethylene (UHMWPE) fibers employing a full wide angle X-ray diffraction (WAXD) pattern. The predominant crystals are orthorhombic form and the refined unit cell dimensions for a and b are 7.40(±0.03) and 4.94(±0.03) A, respectively. The average crystallite size normal to 110 planes was found to be in the range of 163–182 A. The microstrain lattice distortion was predominant in the gel-spun UHMWPE fibers, with the lattice constant variation of 0.5%.